1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device and corresponding driving method that stably performs a write protection function.
2. Discussion of Related Art
Flat panel display devices such as an LCD (Liquid Crystal Display) device, a PDP (Plasma Display Panel), and an ELD (Electro Luminescent Display) are used as display devices in various equipment. The LCD device is most widely used as a portable image display device due to its excellent image quality, its light weight, its slimness, and its low power consumption, and has replaced a cathode ray tube. The LCD device is also being developed as a television monitor, notebook computer monitor, etc.
Further, the LCD device displays an image using the optical anisotropy and the polarity of a liquid crystal. That is, the liquid crystal molecules included in the liquid crystal can be arranged in a predetermined (constant) direction, and the direction of the liquid crystal molecule arrangement can be controlled by applying an electric field to the liquid crystal. Therefore, when the molecule arrangement direction of the liquid crystal is arbitrary, the molecule arrangement can be changed by applying an electric field. In addition, image information can be expressed by changing the polarization of light in the molecule arrangement direction of the liquid crystal using the optical anisotropy.
In more detail, FIG. 1 is a block diagram of an LCD device including a related art overdriving circuit. Referring to FIG. 1, the related LCD device includes a liquid crystal panel 2, a gate driver 4 and a data driver 6 driving the liquid crystal panel 2, and a timing controller 8 controlling the gate driver 4 and the data driver 6. Further, the liquid crystal panel 2 includes a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm crossing the plurality of gate lines GL1 to GLn. The data driver 6 is mounted onto a data printed circuit board (PCB) 18.
In addition, the timing controller 8 includes an overdriving circuit (ODC) 10. The ODC 10 corrects video data for an overdrive operation. That is, the ODC 10 compares the previous frame data supplied form a system (not shown) with the current frame data and detects the difference between the data. The ODC 10 corrects the current frame data according to the difference between the previous and current frame data and supplies the corrected data to the data driver 6.
Also, to calculate the corrected data, the ODC 10 reads a look-up table stored in an external memory device, i.e. the EEPROM 12. In the look-up table, the logic values of the data of the previous and current frames are arranged in the X-axis and the Y-axis, and the correction data for the overdrive operation are disposed at portions at which the X-axis and the Y-axis cross each other. Accordingly, the ODC 10 supplies the previous and current frame data to the EEPROM 12 as a column and row address and reads the correction data from the look-up table of the EEPROM 12. In addition, to read the correction data from the look-up table, the ODC 10 communicates with the EEPROM 112 in the I2C method. That is, in the I2C method, two active wire SCL (Clock) and SDA (Data) (not shown) are connected between the ODC drive section 10 and the EEPROM 12.
Further, as shown in FIG. 1, a voltage generating section 14 supplying a predetermined voltage to the write protection terminal W/P of the EEPROM 12 is mounted to a control PCB 22 together with the timing controller 8 and the EEPROM 12. Also, the control PCB 22 is electrically connected to the data PCB 18 through an FFC (Flexible Flat Cable) 20. In addition, when the EEPROM 12 performs the read function, the ODC 10 in the timing controller 8 reads the correction data from the look-up table in the EEPROM 12 and supplies the correction data to the data driver 6. The data driver 6 then supplies the data voltage corresponding to the correction data to the liquid crystal panel 2 to display an image on the liquid crystal panel 2.
In the LCD device, the correction data are frequently changed according to the characteristics of a user and the sale strategy of a manufacturer. In addition, to conveniently change the correction data, the LCD device uses a recordable and nonvolatile EEPROM 12 as an external memory device. Further, the EEPROM 12 has an input voltage terminal receiving an input voltage Vcc from a predetermined power source supply section (not shown), a write protection terminal W/P, and an SCL (Serial Clock) terminal and an SDA (Serial Address/Data) terminal as I2C terminals for communicating with the ODC 10.
In addition, the function of the EEPROM 12 is determined according to the level of a voltage supplied to the write protection terminal W/P. If a high level voltage is supplied to the write protection terminal W/P, the EEPROM 12 performs only a read function. Meanwhile, if a low level voltage is supplied to the write protection terminal W/P, the EEPROM 12 performs both the read function and a write function.
Further, a voltage generated from the voltage generating section 14 is supplied to the write protection terminal W/P of the EEPROM 12. Also, the voltage generating section 14 divides the power source voltage supplied from the power source supply section by the first and second resistors R1 and R2 (as shown in FIG. 1). The voltage divided by the voltage generating section 14 is supplied to the write protection terminal W/P of the EEPROM 12.
Further, to easily regulate the divided voltage output from the voltage generating section 14 to a high level or a low level, one of the first and second resistors R1 and R2 can be replaced by a variable resistor. Thus, by regulating the resistance value of the variable resistor, the divided voltage output from the voltage generating section 14 can be varied to a high level or a low level.
In addition, before the LCD device is completed as a finished product, the EEPROM 12 should be able to perform the read/write functions so as to store the look-up table from an external writing apparatus. On the other hand, when the LCD device is driven (i.e., after the LCD device is finished), the EEPROM 12 should maintain the write protection state to perform only the read function.
Further, the control of the write protection depends on the voltage supplied to the write protection terminal W/P of the EEPROM 12 (i.e., the voltage divided by the first and second resistors R1 and R2). In other words, the function of the EEPROM 12 is changed (i.e., the write protection is selected) by the power source voltage Vdd determining the voltage to be supplied to the EEPROM 12 and the resistance values of the first and second resistors R1 and R2.
However, the power source voltage Vdd can be distorted by noise and static electricity ESD introduced from the outside. If the distorted power source voltage Vdd is supplied to the voltage generating section 14, the voltage generating section 14 divides the distorted power source voltage Vdd using the first and second resistors R1 and R2. Then, the divided voltage is supplied to the write protection terminal W/P of the EEPROM 12 and causes a malfunction of the EEPROM 12 (i.e., releases the write protection function).
More particularly, if a low level voltage is supplied to the write protection terminal W/P of the EEPROM 12, the write protection function of the EEPROM 12 is released. Then, if the EEPROM 12 performs the write operation, the correction data in the look-up table which has been stored in advance is damaged by the static electricity generated from the outside and the noise.
As mentioned above, because the voltage supplied to the write protection terminal W/P is influenced by the distorted power source voltage Vdd, the write protection function of the EEPROM 12 is influenced by the distortion of the voltage supplied to the write protection terminal W/P. Further, when a voltage of a high level is supplied to the write protection terminal W/P to allow the EEPROM 12 to perform only the read function (when the LCD device is driven), a voltage of a low level is occasionally supplied to the write protection terminal W/P of the EEPROM 12 by the distorted power source voltage Vdd so as to allow the EEPROM 12 to perform the write function. If the EEPROM 12 performs the write function when the LCD device is driven, unintended new data is introduced by an external factor, thereby damaging the data stored in the EEPROM 12.